Dear Valeria ,to have such a big size photos I created an acount by the www.flickr.com.It costs nothing and you can put till 200 photos without to pay nothing.After that you have the choise to upload your photos in 4 different sizes.Some other blogers use also PICASA but I try it without to be able to have big size photos.So I reccoment you Flickr.Many regards and big succes!!